1. Field of the Invention
The present invention relates to an organism information measuring apparatus, such as a pulse-wave measuring apparatus, that is capable of displaying information about the pulse wave, such as the pulse rate. More particularly, the present invention relates to an apparatus that irradiates an organism with light and detects light reflected by the organism to measure information about the organism, such as the pulse waves. In particular, the present invention relates to an arm wear type pulse-wave measuring apparatus that is capable of measuring information about the organism during an exercise, such as jogging, running or cycling.
2. Description of the Related Art
Apparatuses for measuring information about an organism, such as pulse waves, include, in the category thereof, electronic apparatuses of a type that optically detects change in the quantity of blood to display information about an organism in accordance with results of the detection. In an optical pulse-wave measuring apparatus (an organism information measuring apparatus) of the foregoing type, a light emitting device, such as an LED (Light Emitting Diode), irradiates the fingertip or the like with light, and light reflected by the organism (the blood vessel) is received by a light receiving device, such as a phototransistor so that change in the quantity of blood occurring due to the pulse waves of the blood is detected as change in the quantity of the received light. In response to a pulse wave signal obtained from the detection, change in the pulse rate or the pulse waves are displayed. As the light to be emitted from the light emitting device, infrared rays have been employed. If external light (sunlight or the like) is made incident upon the light receiving device, change in the quantity of the external light causes the quantity of received light to be changed. Therefore, the conventional pulse-wave measuring apparatus has a light shielding cover to cover the portion to be detected, such as the fingertip, so that influence of the external light is prevented.
However, if the conventional pulse-wave measuring apparatus has a large light shielding cover, use of the apparatus in a place, such as outdoors, that is irradiated with external light results in that a portion of the external light passes through the finger and reaches the light receiving device. Thus, the conventional pulse-wave measuring apparatus has a problem in that the change in the illuminance of external light causes pulse waves to be detected erroneously. Therefore, the conventional pulse-wave measuring apparatus encounters a limitation in that it can be used only in a place that is not irradiated with external light or a place in which the constant illuminance of external light can be attained. To eliminate the foregoing limitation, a larger-scale light shielding structure must be provided to prevent influence of external light. Therefore, the size of the pulse-wave measuring apparatus cannot be reduced, and therefore the conventional pulse-wave measuring apparatus cannot be used as an apparatus that is able to measure information about pulse waves during exercise, such as jogging, running or cycling.
To overcome the foregoing problem, a pulse-wave sensor has been disclosed in Japanese Utility-Model Laid-Open No. 57-74009 which, in addition to the device for detecting pulse waves, comprises an external-light detection device for detecting external light and which compensates influence of external light in accordance with results of the detection of external light obtained by the external-light detection device. However, provision of the external-light detection device and a compensation circuit for the pulse waves sensor prevents size and cost reductions. As described above, any of the conventional countermeasures against external light has been unsatisfactory in view of practical use.
Furthermore, as a pulse-wave measuring apparatus of the foregoing type, there has been a desire for an arm wear type apparatus that is capable of measuring the pulse rate and the like during jogging, running, cycling or a marathon race. To constitute a pulse-wave measuring apparatus of the foregoing type, a small size sensor unit is required which can be put on the root of the finger. If a small sensor is put on the root of the finger, the user is able to lightly clench the fist.
In view of the foregoing, the inventors of the present invention have performed a variety of investigations for the reason why pulse waves are erroneously detected due to change in the illuminance of external light. As a result, it is concluded that infrared rays for use in the detection system of the conventional pulse-wave measuring apparatus have an excessively large transmittance with respect to the organism that causes external light to easily reach the light receiving device through the organism even if a light shielding cover is provided. Thus, if the foregoing problem can be overcome, a practical countermeasure against external light can be provided.